1. Field of the Invention
This invention concerns a safety relief for relieving the pressure of a gas within a pressure vessel such as an air compressor tank, a pressure tank used in manufacturing or a storage tank used to hold a quantity of gas under pressure.
2. Description of the Related Art
Pressure vessels are used in a wide variety of commercial, industrial and residential applications. For example, pressure vessels are often an important element in power and manufacturing plants. In such settings, pressure vessels provide a structural container for many possible functions including chemical reactions, treating, mixing and blending, separation, heat exchange and regeneration.
Pressure vessels are also used for the storage of a gas under pressure. Common examples of such vessels include cylindrical, barrel-shaped or drum-shaped containers for acetylene, propane, hydrogen, oxygen and carbon dioxide. Typically, gas storage vessels have wall sections that are relatively thick to withstand considerable pressure so that a relatively large amount of gas can be retained within the vessel. Gas storage pressure vessels are useful in many industrial, commercial, farming and residential applications.
Another well-known example of a pressure vessel includes the tank commonly used in connection with air compressors. The tank provides a reservoir for the temporary storage of compressed air so that the air compressor need not operate every time that a relatively small amount of air is withdrawn from the tank. The tank extends the useful life of the air compressor by reducing the number of times that the air compressor would otherwise be energized during intermittent withdrawal of pressurized air over a period of time.
Unfortunately, the energy stored in pressurized gases contained in pressure vessels represents a potential hazard that in certain circumstances can cause serious bodily harm and even death. If, for example, the vessel was manufactured with a welded seam that was relatively weak, the seam might rupture during use, and the force of the escaping gas might cause a fragment of the vessel to injure the operator or a bystander. Moreover, if the stored gas is flammable, the gas could ignite and cause a fire or explosion.
As a consequence, manufacturers of pressure vessels have devoted considerable attention over the years to the construction of vessels that are intended to safely contain gases under certain, pre-designated pressures. In addition, many states and cities of the United States and certain provinces and territories of Canada have adopted all or part of the A.S.M.E. Boiler and Pressure Vessel Code as a legal basis for pressure vessel construction. The A.S.M.E. Boiler and Pressure Vessel Code sets out certain minimum, essential construction requirements for pressure vessels in an effort to ensure that such vessels do not rupture when properly used as intended and correctly maintained.
Pressure relief valves are often used with certain vessels to keep pressure within the vessel below a certain specified limit. As an example, some tanks used in industrial processes to enclose and contain a chemical reaction are provided with a valve that opens to relieve pressure within the tank if the pressure exceeds the specified amount. The relief valve is useful for keeping pressure within the tank below the amount that is considered the maximum for safe operation as may be determined by the manufacturer of the tank.
However, some pressure vessels such as those made of steel may weaken after an extended period of time due to corrosion on an inner surface of the vessel wall. The corrosion may eventually weaken the wall to such an extent that the wall eventually ruptures when the vessel is in use. Such internal corrosion is especially hazardous because the visible, outer surface of the wall may appear relatively unblemished and lead the user to believe that the vessel is in satisfactory condition. As a result, the wall may rupture even though the pressure within the vessel is below the maximum rated pressure of the vessel as was originally determined by the vessel manufacturer.
It is known, for example, that the internal walls of air compressor tanks can corrode due to water vapor that condenses from compressed air in the tanks. Many manufacturers of air compressors attempt to avoid problems of internal corrosion by including a drain valve near the bottom of the tank. Instructions provided with the air compressor direct the user to open the drain valve after each use in order to drain condensed moisture from the tank.
However, the drain valves provided on air compressor tanks have not completely avoided the problems caused by moisture condensing within the tanks, and serious injuries due to rupturing walls of corroded tanks have still been reported. In some instances, the user may not read or fully comprehend the manufacturer's instructions to open the drain valve after each use. In other instances, the user may simply forget to open the drain valve. Many air compressor systems intended for household use maintain pressures of up to 125 p.s.i. or more, which is sufficient to cause significant injury if the tank were to unintentionally rupture.
There is clearly a need in the art to solve the problem of providing a safe pressure vessel in order to avoid personal injury and property damage that might otherwise occur due to internal corrosion of the vessel. Preferably, such a solution should be relatively inexpensive, adaptable to a variety of different vessels and yet require little, if any, attention from the user.